Question

What is the 7th term of the geometric sequence where a1 = -5 and a5 = -1,280?

Answer 1

Any geometric sequence can be expressed as:

a(n)=ar^(n-1), a=initial term, r=common ratio, n=term number.

Here we are give the initial term so we have to solve to solve for the common ratio...

a(5)=-1280 and a(1)=-5 so

-1280=-5r^(5-1)

-1280=-5r^4

256=r^4

256^(1/4)=r

4=r, so our sequence is:

a(n)=-5(4^(n-1)), so the 7th term is:

a(7)=-5(4^6)

a(7)= -20480